1. Field of the Invention:
This invention relates to lasers, and more particularly to a highly repetitively pulsed laser stabilizing device.
2. Description of the Prior Art
An active mode locking laser device in which an A-O element (acousto-optical element) is inserted in the laser resonator, and a passive mode locking laser device in which a saturable absorber such as dye solution is inserted in the laser resonator, are known in the art as examples of highly repetitively pulsed laser devices. However, both have shortcomings regarding the stabilization of the optical pulse output. In the active mode locking laser device, electrical control for stabilization of the ultrasonic strength of the A-O element is intricate. In the passive mode locking laser device, adjustment of the density of the saturable absorber such as dye solution with respect to the magnitude of excitation energy is complicated.
In order to solve the above-described problems, the present applicant has proposed a highly repetitively pulsed laser device in Japanese Patent Application No. 142262/1987, in which a feed-back system, simple both in construction and in adjustment, is provided for the laser resonator. When the optical pulse returning into the laser resonator and the optical pulse in the laser resonator are coincident, the output optical pulse is stable, short, and high in power when compared with that in the prior art.
However, the device is still disadvantageous in that when the laser resonator length changes, with ambient temperature for instance, an optical pulse returning into the laser resonator through the feedback system and an optical pulse in the laser resonator are shifted from each other in the timing of superposition. Therefore, the output optical pulse is shifted from its optimum value.